The aim of this research is to accumulate further knowledge pertinent to the chemical characteristics of pyrimidine adducts, pyrimidine coupled products, the so-called "spore" product, and pyrimidine photohydrates. Such information is essential for the chemical analysis on the ultraviolet radiation damage in cellular DNA. Studies of UV radiation effects of organisms have been focused on pyrimidine dimers and have shown the efficient repair of these dimers in normal cells. Since damage once repaired presumably has no untoward effects on cellular functions, it must be either non-repairable or inefficiently repaired damage that is responsible for the apparent cellular UV sensitivity. Therefore, evaluation of the production, repair, and lethality of UV damage other than dimers, i.e. non-dimeric damage, becomes vitally important.